This invention relates generally to medical implant devices, and more particularly to a biocompatible prosthetic device for the replacement of the mandibular condyle and the mandibular fossa which together form the temporomandibular joint.
A variety of medical conditions in the area of the temporomandibular joint can result in the need for partial or total replacement of this joint. Some of the conditions which may require such a surgical procedure include cases of osteoarthritis, rheumatoid arthritis, traumatic arthritis, malignancy, benign neoplasms, functional deformity, failed total temporomandibular joint arthroplasty, avascular necrosis and ankylosis.
In these types of situations, bone degradation may occur on one or both sides of the temporomandibular joint, namely, in the mandibular fossa region or in the opposing mandibular condyle. Where both the mandibular fossa and the mandibular condyle are degraded through one or more of the above or other conditions, a total temporomandibular joint (hereinafter "TMJ") replacement procedure may be desirable to replace the affected bone portions with prosthetic implant devices.
The natural movement of the temporomandibular joint allows for two distinct movements of the mandible relative to the maxilla. The first movement produces hinging motion in one plane consistent with a ginglymoid joint. The second movement is gliding motion consistent with a arthrodial joint. These movements classify the temporomandibular joint as a ginglymoarthrodial joint. These two motions are created by the involvement of the muscles of mastication, primarily the masseter, temporalis, and pterygoid muscles. As such, the human jaw is able to accomplish circular chewing in at least a limited fashion by combining these distinctive movements.
Prior attempts to reconstruct one or both portions of the temporomandibular joint have encountered several disadvantages. Firstly, some temporomandibular joint implant devices have failed to allow for the limited circular pivoting movement such as that accomplished naturally by the human jaw. In addition, in the case of implant surgery occurring on only one side of the jaw, the range of movement of the replacement joint may not match the range of movement of the remaining natural joint. The range of movement of the jaw as a whole is then largely limited by the artificial side, in the case where the range of movement of the artificial side is less than that of the remaining natural joint.
The natural anatomical shape of the mandibular fossa is an oblong shape, which shape has been duplicated by prior temporomandibular joint implant devices. Prior implant devices have also included the use of oblong shaped condylar head portions for engaging the mandibular fossa. The use of these shapes for temporomandibular joint implant devices, however, resulted in the need for critical placement of both the artificial mandibular fossa component, upon the zygomatic arch, and the artificial condyle upon the ramus relative to each other. As such, the use of oblong shapes for artificial mandibular fossa components and/or artificial condyles may require repeated minute adjustments in these components, which may even include bending these components. This is undesirable both in the extended time period required for accomplishing the surgical procedure, as well as in the possible damage to the prosthetic device components resulting from their manipulation and/or bending during the procedure.
Another disadvantage of prior temporomandibular joint implant devices is that many of these devices are attached upon the present anatomical structure of the region. This is disadvantageous because it increases the change in relative pivoting position and relative jaw position more than is necessary away from the natural position.
A need therefore exists for a biocompatible prosthetic device for the total replacement of the temporomandibular joint which is designed to function most similar to the natural function of the human jaw. A need also exists for such a device to be easily and quickly inserted and adjusted in proper alignment by the surgeon. A need further exists for such a device to allow circular chewing movement, with a minimum of deviation from the natural motion of the mandible and maxilla.